spl: typo fix for SPL_ATF_SUPPORT description

Delete one redundant 'which' for SPL_ATF_SUPPORT description.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>

common/spl/Kconfig

@@ -696,7 +696,7 @@ config SPL_ATF_SUPPORT
 	bool "Support ARM Trusted Firmware"
 	depends on ARM64
 	help
-	  ATF(ARM Trusted Firmware) is a component for ARM arch64 which which
+	  ATF(ARM Trusted Firmware) is a component for ARM arch64 which
 	  is loaded by SPL(which is considered as BL2 in ATF terminology).
 	  More detail at: https://github.com/ARM-software/arm-trusted-firmware